Growing citrus trees indoors holds a special appeal to northern gardeners. There is an exotic attraction to a tree ripened lemon shining in your living room when it is dark and -40 degrees outside. Citrus plants are ornamental, with fragrant flowers, shiny evergreen leaves, and bright colored fruit which can hang on the plant for months.
Citrus trees have been held in high esteem throughout history due to their beauty, healthful properties, and relative rarity in the western hemisphere. Citrus has shown the stubborn inability to prosper in most of Europe and the temperate world.
Climate is the prime factor in the growing of citrus fruit. Citrus requires a long, hot growing season, and minimal winter freezing. Even in the prime U.S. citrus growing areas of California and Florida, the ability to grow different varieties of citrus, and the characteristics of the ripened fruit, vary dramatically. Florida’s hot, humid climate produces fruit which is larger, longer, lighter in color, thinner in rind, juicier, sweeter, and more prone to disease. California’s cool nights and arid climate produces fruit with more acid (better flavor), flatter, thicker rind, meatier, and more color. As a general rule, CA produces fruit for fresh consumption, and FL for juice. Oranges will not turn orange unless it reaches a low of at least 45 degrees F. FL’s juice oranges are often green, which would be unacceptable in today’s’ fresh fruit market.
In selecting citrus as a houseplant, the hardiness of the plant is less important than the number of heat units required for the fruit to mature. Following, is a list of common citrus, and the relative amount of heat required for ripening. Grapefruit require the greatest amount of heat, and kumquats the least.
Grapefruit (long, hot season)
The hardiest part of growing indoor citrus is in not allowing yourself to- buy an edible orange or grapefruit tree. These two fruits both require more heat than is typically found in a home. Three top picks for indoor growing are the calamondin orange (an ornamental orange which is really a mandarin x kumquat cross), the Improved Meyer lemon (which isn’t really a lemon but looks and tastes just like one), and kumquats (which aren’t citrus at all, but in the fortunella family). Kumquats are somewhat the opposite of citrus with a sweet rind and sour flesh. They are eaten whole.
Citrus fruits have been interbred for centuries, and even experts don’t know the genetic make up of many varieties. In his book Oranges, John Mc Phee relates the story of two USDA scientists working on a persian lime breeding project. The scientists planted numerous persian lime seeds in the hopes of obtaining a virus free strain. From these seeds grew trees of sweet oranges, sour oranges, grapefruits, tangelos, lemons, and two persian limes. The scientists were surprised that persian limes were produced at all.
Propagating citrus from sexually produced seeds results in very mixed results, and generally the seedlings take about seven years to produce fruit. Citrus also produces asexual seeds, however, known as nucellar. Nucellar seedlings are essentially clones of the parent. Some citrus varieties, especially those grown for rootstocks, produce up to 95% nucellar seedlings. Unfortunately, these take just as long to produce fruit as the sexual seeds.
The most common way to propagate citrus is through budding. Citrus may also be propagated by grafting, layering, and through cuttings. Many, although not all, citrus varieties are graft compatible, allowing for several types of fruit on a common rootstock.
Following are some guidelines for growing citrus indoors. A plant light is needed if you want ripe fruit (just remember how hard it is to keep flowering plants going indoors). Alternatively, citrus leaves can be excellent in recipes. Lime leaves are just as flavorful as the fruit and are essential for Thai cooking. Lemon and orange leaves make excellent flavorings and teas.
Indoor citrus cultural needs:
- Selection of an appropriate variety. Recommended varieties not previously mentioned include: Dancy tangerine, Otahite orange (which is the same as a Rangpur lime, and actual1y a sour tangerine), Ponderosa lemon, and Bearss lime. The Ponderosa lemon produces grapefruit size fruit, but generally will only set 1 to 2. fruit per plant. Citrus takes from 8 to 14 months for fruit to mature.
- Humidity is needed or no fruit will set. This requirement can be met by using a humidifier, by placing the pot over a tray of pebbles covered with water, or by daily spraying.
- At least 12 hours of supplemental light needed in the winter. The plant does well outdoors in the summer.
- Citrus likes soil high in humus (requires a lot of water), but needs good drainage.
- The plant likes a hot daytime temperature with a 20 degree temperature reduction at night. This fluctuation can be achieved by placing the plant near a cold window and keeping a 75 watt incandescent grow lamp on it during the day. Incandescent lights are a combination of inefficient light producers and inefficient space heaters. By turning both the light off and the home heat down at night, the plants’ micro environment can easily descend from 75 to 50 degrees.
- Fertilize lightly. Be careful when using commercial fertilizers as citrus is sensitive to salt build up. Citrus requires the three main nutrients, phosphorus, potassium, and especially nitrogen. The plants are prone to iron and zinc deficiencies. Iron can be provided by placing a couple of nails in the soil.
- Citrus attracts every insect known to houseplants, probably because exact cultural requirements are difficult to meet. Scale might be the worst pest. You can use your thumbnail or rubbing alcohol to remove temporarily, but nothing seems to work permanently.
In Anchorage, citrus trees may be purchased from Alaska Greenhouse. A 5 inch pot, with a plant in bloom, costs about $15.